I didn't expect specifics on a public forum, just Army, Navy or RAF, officer or not, logs, admin, tech. If you weren't familiar it's just easier for me to say things like who moves more frequently and where, because some jobs have a limited no of locations.
It's not crazy at all to ask this. I've seen a lot of posts along these lines because of the Armed Forces being kind of a closed shop. You regularly see and have contact with a lot of careers that people go into, but it's not like you can get onto a base to see what happens there or meet many military people in real life if you aren't near where they are stationed.
Did he not want to keep in touch whilst away, did he say he couldn't? It's difficult but not impossible to keep in touch; some places ban use of personal mobile phones, but have landlines and issue a phone card with credit, and there's e-blueys, and use of the British Forces Post Office (BFPO) to send letters and parcels to the middle of nowhere (as an aside, if he's away for a few months and open to the idea, sweets, toiletries and magazines are good to send, but check the rules concerning what is allowed). In the context of not contacting you when he gets back, equally, he could be posted to the opposite end of the country to you and just drop out of your life. It's really no different to any other LDR, say if you were dating someone at another uni or who travelled for work, in that anyone who doesn't 'come home at night' could cut off communication at any time. I would just talk to him more about how long he is away for, what his plans are when he gets back, what is coming up next at work. Have you been to visit him on base? If not, it's worth doing; say you want to get a feel for his lifestyle and see how it all fits together with the different sections. If he's a sergeant or above, or an officer, then some of the traditional Messes are an experience, also the formal functions there.
I met my boyfriend whilst were both serving and had a lot of time apart and you know, sometimes it's nothing to do with being in the military and everything to with just being a bloke that they don't talk much or tell you stuff!
I hope this is helping, feel free to ask anything else.